For various medical reasons, such as diagnostic tests or the determination of suitability as a tissue donor, it is often necessary for a physician to obtain a sample of a patient's body tissue. In particular, bone marrow is frequently retrieved for later pathological study. The current procedures and instruments used for obtaining the samples, while not overly complex, almost universally result in excessive patient discomfort and often overly extends the patient's and operator's time, money and effort. In the standard bone marrow procurement protocol, using currently standard instruments, (such as those disclosed in U.S. Pat. No. 4,262,676 to Khosrow Jamshidi), the patient is prepared with a suitable local anesthetic at the appropriate marrow retrieval site. Then, a relatively narrow needle is inserted to obtain an aspirate of only liquid bone marrow material for making slides for examination after staining. This portion of the procedure referred to as the bone marrow aspiration, is relatively less painful than obtaining a bone marrow biopsy.
After the aspirate is obtained and the slides and specimens are prepared, if necessary, a biopsy of the fibrous bone marrow is taken. A significantly wider bore needle having an inner diameter that will house a suitable marrow sample is first prepared with an inner stylet that extends beyond the distal end of the outer needle. The stylet distal end may be cut at an angle, with the leading edge sufficiently sharp to pierce tissue and bone. With the stylet in place within the outer needle, the needle is pushed through the outer layers of flesh until the bone is felt at the tip. The needle and styler are then pushed into the bone approximately 4 or 5 millimeters until the needle appears to be solidly within the bone.
The stylet is then removed from the proximal end of the needle, which opens up the core of the needle to the now-surrounding marrow tissue. The outer needle is then usually advanced another 1 to 2 centimeters at minimum with a slight twisting motion. Often, the distal end of the outer needle will also be provided with an angled cut and sharpened leading edge to easily cut and core the tissue. By providing a slight twisting motion as the needle is advanced, usually with no more than quarter or half turns, an appropriate sample is cored from the marrow tissue and enters the inner passage of the marrow needle.
At this point, the marrow biopsy sample piece is ready to be removed from the patient, although it is important that the biopsy piece remain within the needle as the needle is withdrawn. If the biopsy piece becomes dislodged and falls out the distal end of the biopsy needle, the piece is irretrievably lost. The procedure is then unsuccessful and must be repeated from the beginning.
Various methods have been attempted by physicians to prevent the biopsy piece from dislodging from the outer needle. For example, some physicians, after the needle has entered the bone fully and cored a sample from the marrow, will pull the biopsy needle back a few millimeters and then forward a few millimeters at a different angle than the first insertion. This theoretically will "cut" the biopsy piece at the tip of the needle. Other physicians attempt to dislodge or disrupt the connection between the biopsy piece and the bone by making multiple complete clockwise and counterclockwise rotations of the biopsy needles while within the bone. Some physicians even hit the proximal end of the biopsy needle at its handle in an attempt to mechanically disrupt the connection between the core biopsy specimen and the additional bone.
As can be plainly realized, these manipulations at the end of the procedure, attempts at ensuring that the biopsy piece remains within the needle, can often produce substantial discomfort and anxiety. Sometimes when the bone marrow is very soft, as in patients with osteoporosis, almost all of these attempts are futile because the bone structure is so fragile. Conversely, sometimes when the bone marrow is very fibrotic, which occurs in patients with myelofibrotic diseases or in AIDS patients, it is difficult to dislodge the core biopsy piece, since the bone marrow itself is reinforced by surrounding tissue. In those cases, the cored biopsy piece often remains attached to the bone and is not removed in the biopsy process.
Other attempts at designing a more efficient and successful biopsy needle have met with little or no success, for various reasons, including the complexity of the devices. For example, U.S. Pat. No. 3,605,721 to Hallac, discloses a biopsy needle in which an inner tube has a weakened portion represented by strips extending between distal and proximal portions of the inner tube. The distal portion of the inner tube is adhered to an outer tube and will not rotate. Once a biopsy piece has entered the needle, the proximal portion of the inner tube is rotated, causing the strips to twist together and eventually break off. This twisting motion tends to twist the strips to the tube's center, thus hopefully keeping the biopsy piece proximal of the twisted and broken strips for later removal. This particular biopsy needle is only a disposable device, since the strips are broken or irreversibly warped by plastic deformation during the twisting process. Another disadvantage is the lack of control over the twisting motions or the breakage of the strips. Essentially, the surgeon is left to twist the inner tube until resistance to that twisting is lost, indicating that the strips have severed. There is also no way of releasing the device's grip on tissue during surgery, should any problems arise.
U.S. Pat. No. 5,074,311 to Hasson discloses a biopsy device that includes a pair of inner jaws that can be actuated within the outer needle to "bite off" any biopsy piece that has entered the outer needle. The disadvantages of this device include multiple small mechanical linkages and parts including pivot pins, which are extremely difficult and expensive to assemble and maintain, in addition to the greatly increased chance of mechanical failure which can be costly during a surgical procedure.